The present invention relates to an electrical component pick and placement machine, and more particularly to a surface mount device (SMD) placement system that is used to assemble printed circuit boards (PCB) with surface mount electrical components.
SMD have connection pads instead of elongated leads, and these components are mounted onto board-like panels that are formed on suitable dielectric material and have electrical circuits printed on or otherwise applied to their surface. The printed circuits include connection pads for registration with and electrical connection to corresponding connection pads of the SMD.
The mounting of discrete electrical components onto printed circuit boards by automated means is well known. For a rather extended period of time, the electrical components, such as resistors, capacitors, inductors, and the like, included axial, radial, or in-line leads which extended through holes in the PCBs. Over the years, several types of apparatus had been developed to automate this procedure and thereby increase production. Basically, these machines bend the leads, align the components and their leads with respect to lead holes in the printed circuit board to be populated, and then insert the leads into the appropriate holes. The leads are then bent over or clinched to retain the components on the board prior to a soldering operation which both mechanically and electrically bonds the component to the board. In more recent times, however, the SMD technique was developed which does not require through-hole insertion.
Surface mount devices lack or eliminate the long leads associated with through-hole mounted components. SMD's are finding wide use in the electronic industry, and like their leaded counterparts, require accurate placement on PCB's, or other substrate media, prior to soldering. Accordingly, automatic machines have been developed to accomplish this task.
According to the prior art, as exemplified by U.S. Pat. No. 4,381,601, electronic components such as semiconductor pellets or chips can be temporarily attached to the tip end of an attraction (vacuum) nozzle, held, and automatically oriented by means of a plurality of arms arranged along the outer periphery of the tip end of the sucking nozzle. The held electronic component was then transferred to a predetermined bonding position on a semiconductor device substrate before the arms were opened to bring down the electronic component onto the predetermined bonding position for bonding. Although this apparatus is adequate for the task of picking up and depositing a component, it does not include a reliable and accurate means for transporting the component from an input station to a desired location and in exact registration with connection pads on a PCB.
In U.S. Pat. No. 4,393,579, a device for mounting chip-type electronic components on a substrate is disclosed which is designed to enable accurate positioning and mounting of chip-type components such as SMD in a controlled and reproducible manner. This device includes a slide having a recess for accommodating and transporting a component. The component is linearly movable in a guide between a loading position and an unloading position, and a suction device which is movable in the vertical direction serves to pick up a component from the slide when the latter is in the unloading position, and then move the component downward through a passage in the guide to position the picked-up component onto the substrate located underneath the guide. Although this is an improvement over the previously known art, it still leaves much to be desired in speed of operation and reliability.
In U.S. Pat. Nos. 4,135,630 and 4,290,732, machines are described for picking up electrical components and placing them at desired positions and orientations on a substrate. The pick-up heads of these machines utilize a vacuum or suction tool by which components are held on the pick-up head, and pawls or fingers are used to position the components on the tools. These devices work well with electrical components of a particular size and shape, but such components are not all similar in dimension. At best these machines can handle a small range of sizes of components. However, it is frequently necessary to position a number of components of widely varying sizes and shapes on a single substrate, and the above-noted prior art devices cannot provide sufficient accuracy and reliability with a single pick-up head without manually adjusting or changing the pawls or fingers, which is very inconvenient and time-consuming. Subsequently, this problem has been solved by providing a plurality of pick-up heads, each adapted to pick up a different size range of components.
More recently, a head for handling various sizes of electrical components has been described in U.S. Pat. No. 4,624,050. This device includes a head for handling electrical components, the head including a plurality of orienting jaws mounted for movement toward and away from a component carried on a datum face of a tool on a tool holder when the holder is in one of the datum positions. A key feature of this device is that the jaws have a plurality of spaced sets of cooperating datum faces disposed generally transversely to the plane of the datum face of the tool in the holder. Each set of datum faces are disposed so as to be capable of orienting a component carried by a tool mounted on the tool holder when the holder is at a corresponding one of the datum positions. This allows for the handling of a wider variety of component sizes, but still cannot accurately accommodate an infinite variety of component sizes as may be required in the industry.
In order to eliminate the multiple jaw mechanism while attempting to maintain proper pad alignment, more recent developments have provided pick and placement machines again using only vacuum heads having no jaws. For example, in U.S. Pat. No. 4,858,308, an apparatus is disclosed for mounting small electronic parts such as chip capacitors and the like onto a printed circuit board through a series of work stations which are arranged in a closed-loop fashion at a periphery of a rotary-index table. This apparatus utilizes a plurality of suction devices for picking and placing operations. There is disclosed such an operation where suction pieces have various shapes and sizes to accommodate a wide variety of types and sizes of chips. It is taught that since a suction piece can be exchanged after mounting parts, then while one suction device performs a picking and placing operation of a chip, another suction device exchanges the suction piece to accommodate another chip configuration.
Also in this regard, attention is directed to U.S. Pat. No. 4,866,837 which concerns a dual port alignment assembly station for attaching components to circuit boards. An electrical component, such as a chip, is held by an appropriate robotic mechanism over a printed circuit board, and a dual port placement probe is inserted between the component and the circuit board. The probe is provided with a pair of oppositely directed viewing arrangements which respectively look toward the component and the circuit board. The optical images from the pads on both the component and the circuit board are then detected by respective cameras for the two, and the signals derived from the images obtained by the cameras are processed manually or by a conventional vision system. The system produces signals to drive a robot holding the component.
It should thus be clear that in the prior art in the subject area of interest most schemes require either a movable jaw mechanism or a complicated vacuum arrangement. These schemes generally lack the versatility reliability and accuracy required to handle a large variety of component sizes of SMD's that is needed in the industry. It should therefore also be clear that an accurate and reliable SMD pick and placement machine that does not utilize a jaw mechanism or a complicated viewing or vacuum system will obviate the aforementioned shortcomings and would constitute a significant advancement in the art.